The major purpose of this proposed project shall be to develop a comprehensive protocol for assessing cardiovascular reactivity to stressors, for use in epidemiological and clinical investigations of reactivity and cardiovascular diseases in healthy populations. In order to devise a valid reactivity protocol we intend to establish and evaluate procedures for measuring baseline values, providing appropriate challenge tasks, measuring physiological responses in appropriate subgroups, and relating cardiovascular measures obtained in the laboratory to those obtained under more naturalistic circumstances. Having already explored a large number of reactivity tasks with major population subgroups, we intend to proceed with a single large-scale study in order to examine a sufficient number of subjects to meet the objectives of the RFA. Thus, the proposed study will enroll 240 subjects into a 2 (male, female) X 2 (black, white) X 2 (25-44 years, 55-64 years) X 2 (Miami, Durham) design. Subjects will be compared across a broad range of socioeconomic statuses. Each subject will be scheduled for 3 laboratory sessions lasting less than 60 min each. Sessions 1 and 2 will be 2 weeks apart; session 3 will be 6 months later. During these laboratory sessions subjects will be subjected to a forehead cold pressor stimulus, a video game and an evaluative speech stressor. The tasks were chosen because they are easily administered, capable of eliciting a range of physiologic responses in healthy people, capable of discriminating population subgroups, and appear to be reproducible for the same individual and across different sites. Noninvasive cardiovascular measures to be assessed will include heart rate; cardiac output; peripheral resistance; Heather Index; pre-ejection period; left ventricular ejection period; and systolic, diastolic and mean arterial blood pressure (BP). On the same day as each laboratory reactivity session, subjects will wear an ambulatory impedance and electrocardiogram (ECG) monitor at work and at home. The following day the subject will wear an ambulatory BP monitor at work and at home. Data will be analyzed in terms of stability of baseline values, differences in laboratory reactivity between groups, differences in reactivity patterns between tasks, reliability of responses to tasks across sessions, differences in reactivity as an individual difference variable, and generalizability of reactivity in the laboratory to cardiovascular function observed in more naturalistic settings. In order to accomplish these goals improved procedures will be developed for monitoring impedance cardiographic and ECG activity both in the laboratory as well as in more naturalistic settings.